Field and laboratory studies were conducted to determine if differences existed in pinto bean varietal tolerance to postemergence application of imazethapyr under field conditions; if differences in tolerance were due to differential acetolactate synthase enzyme sensitivity or differences in 14C-imazethapyr absorption, translocation, and metabolism; and the heritability of imazethapyr tolerance in pinto bean. All rates of imazethapyr injured Olathe, Sierra, UI-114, P89405, Aztec, and P90570 pinto bean varieties 7 d after treatment in 1991 and 1992, except 53 g ai ha−1 of imazethapyr applied to Sierra pinto bean in 1991. Olathe was injured more than other varieties in 1991, and physiological maturity of Olathe was delayed more than Sierra in 1991 and 1992. Seed yields of all varieties were not reduced in 1991, and only P90570 had reduced seed yields from 53 g ha−1 of imazethapyr in 1992. Differential sensitivity of the acetolactate synthase enzyme to imazethapyr was not the mechanism of differential varietal response. Olathe pinto bean absorbed and translocated 1.4 and 1.3 times more 14C-imazethapyr, respectively, than Sierra pinto bean 24 h after application. No differences in 14C-imazethapyr metabolism were detected between Olathe and Sierra pinto bean. Broad heritability of imazethapyr tolerance in pinto bean was calculated to be 0.85. The number of genes controlling the inheritance of imazethapyr tolerance in pinto bean was greater than one.